cultivars of native plants

I’m looking for information about whether cultivars of native plants are considered native. I work as a landscape designer and often have to use native plants around the county to follow regulations.

There is no definitive answer to your question, and the notion of what is native is fraught with complications. You may have encountered the recently coined term ‘nativar,’ used to describe cultivated varieties of native species. In the most recent edition of Arthur Kruckeberg’s Gardening With Native Plants of the Pacific Northwest, updated by Linda Chalker-Scott (2019), there is a useful explanation of the differences between natives, varieties, cultivars, and hybrids. In answer to the question of whether cultivars may be used in native gardens, Chalker-Scott says that cultivars can be “naturally occurring forms that are discovered and cultivated for nursery trade, or they may be developed through plant breeding programs.” As to whether cultivars should be used in native gardens, she states that “native purity may be important in special landscape situations such as ecological restoration,” but there is no reason not to use cultivars in home gardens.

Chalker-Scott has written extensively on the use of native plants compared with introduced ones. Her Garden Professors blog post “Native vs. nonnative – can’t we all just get along?” attempts to debunk the tendency “to demonize noninvasive, introduced plants in the absence of a robust body of evidence supporting that view.” Susan Harris of the Garden Rant blog also discussed Chalker-Scott’s writing on the subject, “starting with definition of ‘native’. According to Linda, that here-before-the-Europeans thing isn’t as clear-cut as we think. For example, the Ginkgo biloba is considered an Asian plant, yet its fossils can be found in Washington State, where it grew millions of years ago. […] She lists the well-known benefits (see any source on the subject), but also the missing caveats in almost all discussions of native plants: ‘Unfortunately, many of us live in areas that no longer resemble the native landscapes that preceded development…The combination of urban soil problems, increased heat load, reduced water, and other stresses mean that many native species do not survive in urban landscapes. … When site conditions are such that many native plants are unsuitable, the choice is either to have a restricted plant palette of natives or expand the palette by including nonnative species.'”

The 2019 article “Native vs. ‘nativar’ – do cultivars of native plants have the same benefits?” (from the University of Illinois Urbana-Champaign Extension blog ) explores how we define native, and what the differences are for native pollinators when faced with cultivated varieties. The answer depends on the nature of the variation: plants bred for different colored foliage than the plain species, for instance, may affect whether or not insects will be attracted to it. Benjamin Vogt’s thoughtful and well-illustrated article, “Navigating Amid Nativars” (Horticulture magazine, July/August 2022) encourages us to think in a nuanced way about native plant cultivars. Some may be good for pollinators, but “the more we alter a plant, the more we risk reducing its benefits to the fauna around us.” The benefits and deficits of nativars are not straightforward. He suggests keeping in mind that our home landscapes “are not actually restoring nature [..] in the same way we would in a prairie or forest. Those ecosystems require a larger set of more complex rules and goals.” If your aim is to do the most you can to make a garden function like an ecosystem, “use as many open-pollinated, straight species as you can and […] create thick layers with significant plant density that will prove more resilient to a variety of urban and climatic pressures.”

Native plants, Native plants–Pacific Northwest

A Romance with the Exotic Madrona, Alias of the Arbutus

Roy Martin is a retired University of Washington professor of anesthesiology and bioengineering. He is now pursuing a very different passion, the genus Arbutus, best known locally by A. menziesii, the Pacific Madrone. Eleven species are recognized and in “A Romance with the Exotic Madrona, Alias of the Arbutus,” Martin explores them all, visiting their native ranges in Mexico, western North America, and around the Mediterranean.

This book is very engaging, reading much like a travel journal in places and a history of human culture elsewhere. The author includes a detailed discussion of the common name for our native species, concluding that there are distinction even within our region. In Washington, it is Madrona or Pacific Madrone, while in British Columbia, the name Arbutus is typical.

After exploring the other species, Martin comes home to begin searching for outstanding specimens of A. menziesii. While not abundant, there are several examples of massive trees, hundreds of years old. Martin not only tells the natural history of each tree, as best it is known, but that of the people and locales that surround each.

It is clear that Arbutus menziesii has captured Roy Martin’s heart. “It is not an aggressive tree; it does not, as some trees do, grow rapidly in order to reach the upper stratosphere of the forest and thereby capture most of the available light at the expense of its neighbors. It is, rather, an uncommonly cordial tree, often contorting itself as necessary to find open spaces, through which light falls naturally, as if to accommodate smaller trees it would otherwise effectively starve.”

Excerpted from Brian Thompson’s article in the Spring 2023 issue of the Arboretum Bulletin

Is Diabolo ninebark a PNW native?

I am wondering if Diabolo ninebark is a native to the Pacific Northwest. I know it is a hybrid.

There are several components to consider here. Physocarpus opulifolius ‘Diabolo’ is a cultivar (a cultivated variety, selectively bred for certain characteristics that differ from the plain species) of a ninebark species that is native to eastern North America. A hybrid is produced through sexual reproduction between plants of two different species or varieties, either in the wild or in cultivation. This blog post describes some potential ramifications of using ‘nativars’ (quasi-native plants) such as ‘Diabolo.’ Cultivars are not natives, but that isn’t necessarily a reason to exclude them from your garden. This link provides clear explanations, excerpted here:

“When the native plants in our yards are locally-sourced and locally-adapted, their DNA can make a positive contribution to the survival of wild plant populations. The adaptive genetic diversity they share is important because it allows native species to persist despite the rapidly changing conditions of our modern environment. […]

“When the plants in our yards are cultivars of native species, their genetic makeup is the result of artificial rather than natural selection and they possess little genetic diversity. The offspring of cultivars crossed with native plants are called hybrids. […] Once the DNA from cultivars of native plants makes it into wild populations, there is no way to dispose of it. The new DNA affects the ability of wild native plants to survive and has ramifications for all the species that interact with the native plant as well. Studies have shown that, in some cases, cross-pollination with cultivated varieties resulted in the loss of the wild relative. […]

“Sterile cultivars of native plants are benign, they can’t cross-pollinate with their wild relatives, so they pose no risk to wild plant populations. When cultivars are beneficial to ecosystems, they are good. For example, plant breeders are working to create disease-resistant cultivars of native tree species that have been hit hard by non-native invasive plant pathogens. If done with care, it is possible that such cultivars could be used to intentionally spread beneficial DNA into wild plant populations and help restore those species. […]

“When cultivars are harmful to ecosystems, we must ask whether the benefit to people outweighs the risk to native plant species and pollinator populations. Cultivars of plants aren’t just bred for ornamental use, but for food and medicinal value as well.”

If you want to grow a species of ninebark that is native to the Pacific Northwest, consider Physocarpus capitatus.

Native plants–Pacific Northwest, Physocarpus

Douglas Fir: The Story of the West’s Most Remarkable Tree

There are many rare and unusual trees and shrubs in the Washington Park Arboretum. Standing aside (and sometimes out-competing) these wonderful exotics is the native matrix of trees, especially tall conifers. Perhaps the most iconic of these is the Douglas-fir (Pseudotsuga menziesii). “Douglas Fir: The Story of the West’s Most Remarkable Tree” is a comprehensive new book by Stephen Arno and Carl Fiedler about this tree native from northern British Columbia to the high mountains of Mexico.

There two distinct varieties of the Douglas-fir. The coastal tree (P. m. var. menziesii) that we are familiar with in Seattle and is found along the coast south to the California Bay Area. The inland variety (P. m. var. glauca) has an even wider distribution east of the coastal ranges and into the Rocky Mountains. The ecological success of both varieties highlights their adaptability, supported by an extra set of chromosomes when compared to most of the other West Coast conifers. In simple terms, this means the “Douglas-fir is nature’s all-purpose tree.”

This malleable nature has caused more than its share of nomenclature issues. Is it a fir? A pine? A spruce? The answer is none of the above. The genera Pseudotsuga translates as “false hemlock” – a rather unfortunate compromise. Even the common name has varied, although the Seventh International Botanical Congress in 1950 settled on “Douglas-fir” and that form is used throughout this book (although the hyphen is oddly missing from the book’s title).

The coast Douglas-fir is one of the tallest plant species in the world. Its loftiest example (at 327’) currently ranks number three behind the height champions of the Coast Redwoods (Sequoia sempervirens at 380.3’) and Eucalyptus regnans (329.7’) of southeastern Australia. An especially engaging part of this book discusses the credible possibility of historical Douglas-fir specimens, taken down for lumber one hundred or more years ago, that likely exceeded 400’ in height.

While Euro-Americans quickly recognized the value of Douglas-fir wood for building, the indigenous people throughout the tree’s vast range were the first to use its timber this way, but they had many other uses, too. All parts of the tree are valuable and were used for preserving and flavoring food, for medicine, for crafting tools, in sacred ceremonies, and most importantly, providing heat. “Both varieties of Douglas-fir historically fulfilled myriad roles for native peoples and were the overwhelming choice for one critical daily need: fuel for their fires.”

Excerpted from the Spring 2021 issue of the Arboretum Bulletin

Native Plants PNW

An encyclopedia of Pacific Northwest native plants with information on range, habitat, identification, and use by people and animals.

Native plants in the coastal garden

“Native Plants in the Coastal Garden” (1996, revised 2002) by April Pettinger and Brenda Costanzo brings a British Columbia focus to native plant gardening. Essays describe the rise of a late 20th century naturalistic aesthetic in European and American garden design and the supreme suitability of native plants for this look. Many different design aspects are considered, such as container gardening with native plants, and the large role that grasses play in any landscape.

Only in the latter half of the book are species described in depth, presented in groupings by appropriate habitats. Trees, shrubs, and herbaceous plants have equal treatment with a section for each on propagation and cultivation. Photos are limited and most of the information on nurseries and public gardens is out of date.

Excerpted from the Summer 2019 Arboretum Bulletin.

Gardening with native plants of the Pacific Northwest

Art Kruckeberg (1920-2016) has a legendary reputation for his research and teaching in botany, and his expansion of that work into the natural history and geology of selected ecosystems. But for gardeners, he is best remembered for his classic “Gardening with Native Plants of the Pacific Northwest,” first published in 1982, followed by a second edition in 1996.

Linda Chalker-Scott is rapidly developing her own renown for books that encourage learning the science behind growing plants. Now she has taken on the major task of guiding the publication of a third edition of “Gardening with Native Plants of the Pacific Northwest.”

This is not just an editorial update. It is a collaboration from different perspectives and eras. Kruckeberg was a professor of botany for nearly four decades at the University of Washington until his retirement in 1989. In his first edition, he acknowledges the help of several individuals that figure prominently in the mid to later 20th century Arboretum, including Brian Mulligan, Roy Davidson, Joe Witt, C. Leo Hitchcock, Sylvia Duryee, and his wife, horticulturist Mareen Kruckeberg, the latter credited with conceiving the concept of this book.

Chalker-Scott is an associate professor of horticulture and extension specialist at Washington State University. Her contributions to the new edition further enhance the reader’s understanding of our native plants in their natural setting, and how to make them thrive in the not-very-natural setting of a typical home garden.

For those familiar with the older editions, the first thing you’ll notice in the new edition is the inclusion of many color photographs, almost one for every text entry. Each photograph has a selection of habitat icons “to help gardeners both visualize the best natural settings for native plants and identify environmental preferences.” For example, a plant may naturally grow in the full sun of a meadow or prairie, or it may need the superb drainage of a rock garden. Plants may be best adapted for wetlands or drylands, or perhaps a woodland or even a seashore. Another symbol marks plants especially successful in restoration projects. The new edition also updates taxonomy, reflecting the recent publication of the 2nd edition of the “Flora of the Pacific Northwest” (see my review in the Spring 2019 issue of “The Bulletin”).

For those new to this book, the breadth of the plant selection may be surprising – we have many garden-worthy natives. The emphasis is on woody plants. Almost all native trees are reviewed in some depth, including those not recommended for a garden setting. In the chapter on deciduous shrubs, ten “choice” species are considered first as the best choices. Much of the writing in these plant descriptions is the voice of Kruckeberg, although I noticed that favored plants are now “our” favorites – the two authors agree on most of the selections.

Chalker-Scott has added a new chapter that brings her signature work on horticultural science to the establishment and maintenance of a garden rich in native plants. She alleviates concerns about using “nativars” – propagated selections chosen for an unusual and desirable trait, such as double flowers or variegation. She also assures the new gardener that it is okay to mix well-behaved exotics into your garden of mostly natives.

One major difference between the second and third editions is the removal of any instructions on how to collect native plants from the wild. Chalker-Scott cautions, “This practice must stop if we are to retain many of our rare, threatened, and endangered species. It’s a better ethical and ecological choice to purchase native plants from reputable nurseries that have propagated and cultivated their plants without endangering native populations.”

Excerpted from the Summer 2019 Arboretum Bulletin

Flora of the Pacific Northwest : an illustrated manual

For Pacific Northwest botanists of all levels, the one-volume book informally known as “Hitchcock” has been standard equipment since its publication in 1973. This work, “Flora of the Pacific Northwest: An Illustrated Manual” by C. Leo Hitchcock and Arthur Cronquist, was intended as a field version of the five-volume flora “Vascular Plants of the Pacific Northwest,” written by the same authors with two additional botanists and two illustrators from 1955-1969.

“No scholarly endeavors are immune to the advancing frontiers of knowledge.” This quote is from the introduction of the new, second edition of the one-volume “Flora,” expanded by a team of four editors with three new illustrators. Changes in taxonomy, especially from molecular studies, plus newly described taxa and the establishment of non-native species (which this flora includes) have created a long overdue need for an update.

In the 45 years between publications, there has been a nearly 25% increase in the number of taxa included, the biggest single reason being “the establishment, or detection, of additional exotic taxa within our area.” While this work does not introduce any new names or classifications, just keeping up with widely accepted taxonomic changes has resulted in over 40% of the listings in the first edition having a new genus and/or species name, or being placed in a different family.

Hitchcock was a long-time professor of botany at the University of Washington. He was also a gardener, and many references remain in the 2nd edition regarding the ornamental qualities and garden adaptability of the subjects.

These include the observation that the incense-cedar (Calocedrus decurrens) is a fine ornamental tree, and that “trilliums are rather easily grown, and T. ovatum in particular is an excellent garden pl [plant], but it is a shame to dig them in the wild, esp [especially] since they grow readily from seed.” This urging of conservation (as well as the use of abbreviations) is a repeated theme: “The lilies are a constant temptation to the avaricious gardener, but our spp. [species] rarely thrive in cult [cultivation] and should not be removed from the wild.”

Like the first edition, this book attempts to be comprehensive in its presentation of species, subspecies, and varieties throughout Washington, much of Oregon and Idaho, the western part of Montana, and southern British Columbia. The first edition introduced the new (at the time) idea of embedding the species descriptions and illustrations within the taxonomic keys. This proved to be a good decision. It has remained a best-seller for the University of Washington Press for the last four decades.

At 882 pages (the first edition had 730), it is perhaps a bit hefty for field work, but this is a must for your home garden library. The aforementioned use of abbreviations keeps it from becoming even bigger, and this is a bit of a challenge for reading at first. But after a while, this shorthand becomes familiar. The Miller Library has a lending copy of the new edition, and keeps non-circulating copies of both editions and the earlier volumes of “Vascular Plants.” Be sure to take a look at this new standard for our regional botany!

Excerpted from the Spring 2019 Arboretum Bulletin.

King County, Northwest Yard and Garden

A collections of resources for sustainable yard and garden care. Find information on rain barrels, making compost, Northwest native plants and listen to episodes of the Yard Talk podcast.

Oregon State University: Trees of the Pacific Northwest

This site provides assistance with identifying common conifers in the Pacific Northwest. It includes information about specific genera, user-friendly dichotomous keys, and a mystery tree section where you can test your knowledge.